Quantum enabled operation of a microwave-optics interface*

Superconducting qubits and semiconductor spin systems are some of the most promising candidates for scalable, high clock speed quantum computing. Connecting many such microwave nodes to implement a high-density quantum network remains an open challenge. Since telecom wavelength light is the ideal choice to transfer quantum information at room temperature, there has been a lot of development in microwave-optical transduction. Nevertheless, quantum-limited coherent conversion remained elusive due to either low total efficiency or pump induced heating. We present a quantum-enabled interface between itinerant microwave and optical light. We use a pulsed electro-optic whispering gallery mode transducer to demonstrate nanosecond timescale control of the complex mode amplitude with an input added noise of only 0.16 (1.11) quanta for the microwave-to-optics (reverse) direction.  Working close to unity cooperativity with all involved modes close to their quantum ground state, we observe not only laser cooling of a superconducting microwave mode but also parametrically amplified vacuum noise. This new field of quantum-limited microwave photonics offers many new possibilities ranging from multiplexed classical control to long distance quantum interconnects.